The present invention relates to a method of fabricating a biocompatible material having a relatively high concentration of a carbide or carbon constituent which may be used in the fabrication of medical components, and to such material.
Medical components, such as medical implant components, may be formed or fabricated from a material or materials having good wear properties. As an example, such components may be formed or fabricated from a biocompatible material such as cobalt chrome or a cobalt chrome alloy having a carbide content. For medical implant components, such carbide content may comprise a relatively small percentage of the final material, such as typically only approximately 3-5% by weight thereof. Although the percentage of the carbide content of some biocompatible materials other than cobalt chrome or a cobalt chrome alloy for use in non-medical implant type components may be higher, the size of the particles of carbide therein may be relatively large. As hereinafter more fully described, such relatively large size carbide particles may have undesirable effects.
The carbide content is primarily responsible for the good wear properties of the above-mentioned cobalt chrome alloy. As is to be appreciated, if the percentage of carbide content in a material (such a cobalt chrome alloy) could be increased, then the wear properties of the resultant alloy or material could be improved. However, increasing the carbide content may result in a decrease of other properties. For example, increasing the carbide content in a biocompatible material (such as cobalt chrome) may reduce the fatigue life, strength, corrosion resistance, and toughness, may produce a material which is relatively highly brittle, and/or may reduce the uniformity of the material and produce a material which is relatively highly non-uniform.
The decrease in the above-identified properties (especially the uniformity) may make the resultant material difficult to machine. More specifically, if the carbide content is increased beyond a certain amount, the carbide content in the biocompatible material may not completely mix with the biocompatible material. As a result, the biocompatible material may have some of the carbide constituent or particles completely mixed therein and may have some of the carbide particles which are not completely mixed or not at all mixed therein. Such situation may be considered similar to that of adding sugar to a glass of water. In this later situation, after a certain amount of sugar is added, the sugar no longer mixes or dissolves in the water. Instead, some of the sugar remains in a non-dissolved or a not completely dissolved state.
To further describe the above-mentioned machining difficulty of a material having an increased carbide content, consider the parts illustrated in FIGS. 3A and 3B. With reference to FIG. 3A, unmixed carbide particles 90 contained within an item 92 formed from biocompatible material and carbide may be relatively large, such as between 5-20 microns in size or length. Additionally, the carbide particles 90 may be relatively strong. As a result, machining or cutting such material may be difficult if not impossible. For example, and with reference to FIG. 3B, if a surface 94 of the item 92 to be machined contains a number of relatively large carbide particles 90, then during a machining operation thereof when a cutting tool 96 encounters a portion 98 of a respective carbide particle 90, instead of just the desired portion of such carbide particle being cut, the entire particle may be removed thereby leaving a depression in the surface. As such, it may be very difficult, if not impossible, to properly machine surface 94 (having the relatively large size carbide particles 90) to a desired thickness or dimension T. In other words, even if the item 92 is actually machined so as to have thickness/dimension T, the machined surface may contain a number of depressions or voids and, as such, may not have a desired surface roughness or finish. Additionally, since the carbide particles 90 are relatively strong, the cutting tool 96 may be damaged during the machining or cutting operation.
Thus, merely increasing the carbide content such as in an as-cast cobalt chrome molygdmum (CoCrMo alloy) may result in a decrease in several properties (such as fatigue life, strength, corrosion resistance, and toughness)) and may produce a material having relatively large sized carbide particles which may cause a machining operation to be difficult.
In any event, and possibly for the reasons described above, a biocompatible material such as cobalt chrome or a cobalt chrome alloy having a relatively high carbide content has not been provided to date which may be used in the fabrication of medical components.
It would be advantageous to provide a technique for producing a biocompatible material or alloy, which may be used in the fabrication of medical implant components, having a carbide content of approximately 10% or higher by weight, in which the size of a carbide particle is approximately 900 nanometers or less so as to increase the wear properties of the medical implant components as compared to that of conventional medical implant components and to enable relatively easy machining thereof. It would be further advantageous to provide such technique whereby the resultant biocompatible material or alloy would have relatively good fatigue properties, would not be highly brittle, and would be relatively uniform or homogeneous.